5,793 research outputs found
Separated Fringe Packet Observations with the CHARA Array III. The Very High Eccentricity Binary HR 7345
After an eleven year observing campaign, we present the combined
visual{spectroscopic orbit of the formerly unremarkable bright star HR 7345 (HD
181655, HIP 94981, GJ 754.2). Using the Separated Fringe Packet (SFP) method
with the CHARA Array, we were able to determine a difficult to complete orbital
period of 331.609 +/- 0.004 days. The 11 month period causes the system to be
hidden from interferometric view behind the Sun for 3 years at a time. Due to
the high eccentricity orbit of about 90% of a year, after 2018 January the
periastron phase will not be observable again until late 2021. Hindered by its
extremely high eccentricity of 0.9322 +/- 0.0001, the double-lined
spectroscopic phase of HR 7345 is observable for 15 days. Such a high
eccentricity for HR 7345 places it among the most eccentric systems in catalogs
of both visual and spectroscopic orbits. For this system we determine nearly
identical component masses of 0.941 +/- 0.076 Msun and 0.926 +/- 0.075 Msun as
well as an orbital parallax of 41.08 +/- 0.77 mas.Comment: 20 pages, 3 figures, 4 table
An interferometric study of the post-AGB binary 89 Herculis I Spatially resolving the continuum circumstellar environment at optical and near-IR wavelengths with the VLTI, NPOI, IOTA, PTI, and the CHARA Array
Binary post-AGB stars are interesting laboratories to study both the
evolution of binaries as well as the structure of circumstellar disks. A
multiwavelength high angular resolution study of the prototypical object 89
Herculis is performed with the aim of identifying and locating the different
emission components seen in the SED. A large interferometric data set,
collected over the past decade and covering optical and near-IR wavelengths, is
analyzed with simple geometric models. Combining the interferometric
constraints with the photometry and the optical spectra, we reassess the energy
budget of the post-AGB star and its circumstellar environment. We report the
first (direct) detection of a large (35-40%) optical circumstellar flux
contribution and spatially resolve its emission region. Given this large amount
of reprocessed and/or redistributed optical light, the fitted size of the
emission region is rather compact and fits with(in) the inner rim of the
circumbinary dust disk. This rim dominates our K band data through thermal
emission and is rather compact, emitting significantly already at a radius of
twice the orbital separation. We interpret the circumstellar optical flux as
due to a scattering process, with the scatterers located in the extremely
puffed-up inner rim of the disk and possibly also in a bipolar outflow seen
pole-on. A non-LTE gaseous origin in an inner disk cannot be excluded but is
considered highly unlikely. This direct detection of a significant amount of
circumbinary light at optical wavelengths poses several significant questions
regarding our understanding of both post-AGB binaries and the physics in their
circumbinary disks. Although the identification of the source of
emission/scattering remains inconclusive without further study on this and
similar objects, the implications are manifold.Comment: Accepted for publication in A&A, 16 pages, 15 figure
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Adaptability of Closed-Loop during Labour, Delivery and Postpartum: A secondary analysis of data from two randomized crossover trials in type 1 diabetes pregnancy
Background: Tight glucose control during labour and delivery is recommended for pregnant women with type 1 diabetes. This can be challenging to achieve using the current treatment modalities. The automated nature of closed-loop and its ability to adapt to real-time glucose levels make it well suited for use during labour, delivery and the immediate postpartum period.
Methods: We report observational data of participants from two randomized crossover trials who chose to continue using closed-loop during labour, delivery and postpartum. Labour was defined as the 24 hours prior to delivery and postpartum as the 48 hours after delivery. The glucose target range during pregnancy was 3.5-7.8mmol/L (63-140mg/dL) and 3.9-10mmol/L (70-180mg/dL) after delivery.
Results: Twenty-seven (84.4%) of the potential 32 trial participants used closed-loop through labor, delivery, and postpartum. Use of closed-loop was associated with 82.0% (IQR 49.3,93.0) time-in-target range during labor and delivery and a mean glucose of 6.9±1.4mmol/L (124±25mg/dL). Closed-loop performed well throughout vaginal, elective and emergency caesarean section deliveries. Postpartum, women spent 83.3% (IQR 75.2,94.6) time-in-target range (3.9-10.0mmol/L [70-180mg/dL]), with a mean glucose of 7.2±1.4mmol/L (130±25mg/dL). There was no difference in maternal glucose concentration between mothers of infants with and without neonatal hypoglycemia (6.9±1.6 and 6.8±1.1 mmol/L [124±29 and 122±20mg/dL] respectively; p=0.84).
Conclusions: Automated closed-loop insulin delivery is feasible during hospital admissions for labour, delivery and postpartum. Larger scale studies are needed to evaluate its efficacyThe trials were funded by the National Institute for Health Research (HRM Career Development Fellowship, CDF-2013-06-035), Diabetes UK (BDA 07/0003551), Gates Cambridge Trust PhD fellowship (ZAS), Jean Hailes for Women’s Health (ZAS); Allen-Carey Scholarship in Women’s Health (JMY) and a grant from the NIHR Cambridge Biomedical Research Centre (RH). Abbott Diabetes Care supplied discounted CGM devices, sensors, and details of communication protocol to facilitate real-time connectivity. HRM conducts independent research supported by the National Institute for Health Research
The fundamental parameters of the roAp star 10 Aql
Due to the strong magnetic field and related abnormal surface layers existing
in rapidly oscillating Ap stars, systematic errors are likely to be present
when determining their effective temperatures, which potentially compromises
asteroseismic studies of these pulsators. Using long-baseline interferometry,
our goal is to determine accurate angular diameters of a number of roAp targets
to provide a temperature calibration for these stars. We obtained
interferometric observations of 10 Aql with the visible spectrograph VEGA at
the CHARA array. We determined a limb-darkened angular diameter of
0.275+/-0.009 mas and deduced a linear radius of 2.32+/-0.09 R_sun. We
estimated the star's bolometric flux and used it, in combination with its
parallax and angular diameter, to determine the star's luminosity and effective
temperature. For two data sets of bolometric flux we derived an effective
temperature of 7800+/-170 K and a luminosity of 18+/-1 L_sun or of 8000+/-210 K
and 19+/-2 L_sun. We used these fundamental parameters together with the large
frequency separation to constrain the mass and the age of 10 Aql, using the
CESAM stellar evolution code. Assuming a solar chemical composition and
ignoring all kinds of diffusion and settling of elements, we obtained a mass of
1.92 M_sun and an age of 780 Gy or a mass of 1.95 M_sun and an age of 740 Gy,
depending on the considered bolometric flux. For the first time, we managed to
determine an accurate angular diameter for a star smaller than 0.3 mas and to
derive its fundamental parameters. In particular, by only combining our
interferometric data and the bolometric flux, we derived an effective
temperature that can be compared to those derived from atmosphere models. Such
fundamental parameters can help for testing the mechanism responsible for the
excitation of the oscillations observed in the magnetic pulsating stars
Fundamental Properties of Cool Stars with Interferometry
We present measurements of fundamental astrophysical properties of nearby,
low-mass, K- and M-dwarfs from our DISCOS survey (DIameterS of COol Stars). The
principal goal of our study is the determination of linear radii and effective
temperatures for these stars. We calculate their radii from angular diameter
measurements using the CHARA Array and Hipparcos distances. Combined with
bolometric flux measurements based on literature photometry, we use our angular
diameter results to calculate their effective surface temperatures. We present
preliminary results established on an assortment of empirical relations to the
stellar effective temperature and radius that are based upon these
measurements. We elaborate on the discrepancy seen between theoretical and
observed stellar radii, previously claimed to be related to stellar activity
and/or metallicity. Our preliminary conclusion, however, is that convection
plays a larger role in the determination of radii of these late-type stars.
Understanding the source of the radius disagreement is likely to impact other
areas of study for low-mass stars, such as the detection and characterization
of extrasolar planets in the habitable zones.Comment: Contribution to Proceedings of Cool Stars 16 Workshop; 8 pages in ASP
format; 9 figure
Multiplicity of Galactic Cepheids from long-baseline interferometry I. CHARA/MIRC detection of the companion of V1334 Cygni
We aim at determining the masses of Cepheids in binary systems, as well as
their geometric distances and the flux contribution of the companions. The
combination of interferometry with spectroscopy will offer a unique and
independent estimate of the Cepheid masses. Using long-baseline interferometry
at visible and infrared wavelengths, it is possible to spatially resolve binary
systems containing a Cepheid down to milliarcsecond separations. Based on the
resulting visual orbit and radial velocities, we can then derive the
fundamental parameters of these systems, particularly the masses of the
components and the geometric distance. We therefore performed interferometric
observations of the first-overtone mode Cepheid V1334 Cyg with the CHARA/MIRC
combiner. We report the first detection of a Cepheid companion using
long-baseline interferometry. We detect the signature of a companion orbiting
V1334 Cyg at two epochs. We measure a flux ratio between the companion and the
Cepheid f = 3.10+/-0.08%, giving an apparent magnitude mH = 8.47+/-0.15mag. The
combination of interferometric and spectroscopic data have enabled the unique
determination of the orbital elements: P = 1938.6+/-1.2 days, Tp = 2 443
616.1+/-7.3, a = 8.54+/-0.51mas, i = 124.7+/-1.8{\deg}, e = 0.190+/-0.013,
{\omega} = 228.7+/-1.6{\deg}, and {\Omega} = 206.3+/-9.4{\deg}. We derive a
minimal distance d ~ 691 pc, a minimum mass for both stars of 3.6 Msol, with a
spectral type earlier than B5.5V for the companion star. Our measured flux
ratio suggests that radial velocity detection of the companion using
spectroscopy is within reach, and would provide an orbital parallax and
model-free masses.Comment: Published in A&
Imaging the Algol Triple System in H Band with the CHARA Interferometer
Algol (Beta Per) is an extensively studied hierarchical triple system whose
inner pair is a prototype semi-detached binary with mass transfer occurring
from the sub-giant secondary to the main-sequence primary. We present here the
results of our Algol observations made between 2006 and 2010 at the CHARA
interferometer with the Michigan Infrared Combiner in the H band. The use of
four telescopes with long baselines allows us to achieve better than 0.5 mas
resolution and to unambiguously resolve the three stars. The inner and outer
orbital elements, as well as the angular sizes and mass ratios for the three
components are determined independently from previous studies. We report a
significantly improved orbit for the inner stellar pair with the consequence of
a 15% change in the primary mass compared to previous studies. We also
determine the mutual inclination of the orbits to be much closer to
perpendicularity than previously established. State-of-the-art image
reconstruction algorithms are used to image the full triple system. In
particular an image sequence of 55 distinct phases of the inner pair orbit is
reconstructed, clearly showing the Roche-lobe-filling secondary revolving
around the primary, with several epochs corresponding to the primary and
secondary eclipses
The Ages of A-Stars I: Interferometric Observations and Age Estimates for Stars in the Ursa Major Moving Group
We have observed and spatially resolved a set of seven A-type stars in the
nearby Ursa Major moving group with the Classic, CLIMB, and PAVO beam combiners
on the CHARA Array. At least four of these stars have large rotational
velocities ( 170 ) and are expected to
be oblate. These interferometric measurements, the stars' observed photometric
energy distributions, and values are used to computationally
construct model oblate stars from which stellar properties (inclination,
rotational velocity, and the radius and effective temperature as a function of
latitude, etc.) are determined. The results are compared with MESA stellar
evolution models (Paxton et al. 2011, 2013) to determine masses and ages. The
value of this new technique is that it enables the estimation of the
fundamental properties of rapidly rotating stars without the need to fully
image the star. It can thus be applied to stars with sizes comparable to the
interferometric resolution limit as opposed to those that are several times
larger than the limit. Under the assumption of coevality, the spread in ages
can be used as a test of both the prescription presented here and the MESA
evolutionary code for rapidly rotating stars. With our validated technique, we
combine these age estimates and determine the age of the moving group to be 414
23 Myr, which is consistent with, but much more precise than previous
estimates.Comment: Accepted by Ap
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